Method of forming thin film, substrate having thin film formed by the method, photoelectric conversion device using the substrate

ABSTRACT

The present invention provides a method of forming a thin film containing a metal oxide as the main component, the film thickness of which is relatively uniform, at a high film deposition rate over a wide area and over a long time. The present invention is a method for forming a thin film containing a metal oxide as the main component on a substrate using a mixed gas stream containing a metal chloride, an oxidizing material, and hydrogen chloride, by a thermal decomposition method at a film deposition rate of 4500 nm/min. or greater, performing at least one selected from: 1) prior to mixing the metal chloride and the oxidizing material in the mixed gas stream, contacting hydrogen chloride with at least one selected from the metal chloride and the oxidizing material, and 2) forming a buffer layer in advance on a surface of the substrate on which the thin film containing a metal oxide as the main component is to be formed.

This application is a continuation of U.S. application Ser. No.10/496,487, filed Jun. 3, 2004, which is a National Stage ofPCT/JP02/12683, filed Dec. 3, 2002, which applications are incorporatedherein by reference.

TECHNICAL FIELD

This invention relates to a method of forming, on a surface of a glasssheet or the like, a thin film containing a metal oxide as the maincomponent using a thermal decomposition method. The invention alsorelates to a substrate provided with the thin film formed by thismethod. The invention further relates to a photoelectric conversiondevice using the substrate provided with the thin film.

BACKGROUND ART

A thin film containing a metal oxide such as tin oxide has the functionof reflecting infrared rays. Since a glass sheet provided with this thinfilm reduces the total solar energy transmittance and does not allow theheat within rooms to escape to the outdoors, it is widely available inthe market as a low-emissivity glass. This thin film also can exhibitthe function of shielding electro-magnetic waves. A known method formanufacturing a glass sheet of this kind is such that a thin film of ametallic compound is formed on a high temperature glass surfaceutilizing thermal decomposition methods, such as a chemical vapordeposition method (CVD method) and a spraying method in which a solutionmaterial or a solid material is sprayed. For example, JP 11(1999)-509895A describes a method of forming a thin film of a tin oxide by supplyinga gaseous reaction mixture containing an organic tin compound, hydrogenfluoride, oxygen, and water onto a high temperature glass surface. JP6(1994)-47482 A describes a method of forming a thin film of tin oxideby supplying a vapor of an organic tin compound on a glass ribbonsurface in a float bath in a float manufacturing process. The use of theorganic tin compounds such as described in these patent publications asa raw material for a thin film has an advantage that the thickness ofthe thin film easily is made uniform. Nevertheless, because organic tincompounds have high environmental loads as with tributyltin compounds,the use of alternative raw materials that replace organic tin compoundshas been desired in recent years. Meanwhile, tin chloride conventionallyhas been used widely as a raw material for a tin oxide thin film inthermal decomposition methods. For example, JP 2(1990)-175631 Adescribes a method of forming a coating film in which, with a CVDmethod, a first flow of tin tetrachloride and a second flow of watervapor are supplied onto a glass in a turbulent flow state. Also, JP9(1997)-40442 A describes a chemical vapor deposition method of forminga tin oxide on a glass of a substrate by causing tin tetrachloride andwater to react with each other, wherein tin tetrachloride and water aresupplied by separate flows at temperatures in a range of 100° C. to 240°C. and a single flow is formed and directed to the substratesubstantially with a laminar flow to cause them to react with each otherin a substrate region, whereby the glass is coated.

Such methods of forming a thin film containing a metal oxide thatutilize thermal decomposition methods are inferior to physical vapordeposition methods, such as a sputtering method, in that it is difficultto obtain a uniform film thickness; nevertheless, they are capable offorming a thin film over a wide area within a short time at a relativelyuniform thickness and therefore are suitable for mass production ofindustrial products. With the thermal decomposition methods, generally,the higher the temperature of the reaction system is, the faster thefilm deposition rate, although the situations vary somewhat depending onthe compositional components of the raw materials for the thin film orthe like. Accordingly, it seems that higher temperatures are preferablefor the formation of a thin film in industrial production processes.

In the above-described thermal decomposition methods, the use ofalternative raw materials has been desired because organic tin compoundshave large environmental loads. The present inventors carried out afurther experiment on the method described in JP 2(1990)-175631 A, whichuses tin tetrachloride, an inorganic tin compound, and as a result foundthat when a first flow of tin tetrachloride and a second flow of watervapor are separately supplied to react with each other on a substrate,or when a reaction gas stream is supplied with a turbulent flow,non-uniformity in film thickness is caused in the formed thin film. Thepresent inventors also performed a further experiment on the methoddescribed in JP 9(1997)-40442 A, in which tin tetrachloride and waterare mixed and supplied onto a glass substrate with a laminar flow. Itwas confirmed that it was true that performing a coating according tothis method eliminates non-uniformity in film thickness. However, due tohigh reactivity of tin tetrachloride with water, even when a pipe or thelike for the mixed gas was controlled at a temperature of 100° C. to240° C. as described in JP 9(1997)-40442 A, the pipe was clogged up bythe reactant that deposited inside the pipe after only about 3 hour'ssupplying of a mixed gas of tin tetrachloride and water, making furthergas supply impossible. Then, hydrogen chloride was further added to themixed gas of tin tetrachloride and water vapor, and the mixed gas wassupplied, as described likewise in Example D of JP 9(1997)-40442 A. Inthis case, hydrogen chloride acted as a reaction inhibitor, so the pipewas not clogged up in a short time. Nevertheless, although the cloggingof pipe did not occur when hydrogen chloride and tin tetrachloride weresupplied at a mole ratio of 1:1 as in Example D of JP 9(1997)-40442 A,the film deposition rate considerably lowered to about ⅓ of that in thecase in which hydrogen chloride is not mixed because hydrogen chlorideserved as a reaction inhibitor.

DISCLOSURE OF THE INVENTION

This invention has been accomplished in view of the foregoing problems.Its object is to provide a method of forming a thin film containing ametal oxide as the main component having a relatively uniform filmthickness over a wide area and a long time at a high film depositionrate, by utilizing a thermal decomposition method using an inorganicmetal chloride, which has a low environmental load, as a raw material.Another object is to provide a substrate having this thin film, and toprovide a photoelectric conversion device utilizing this substrate.

In order to accomplish the foregoing objects, a thin film-forming methodaccording to this invention is a method of forming a thin filmcontaining a metal oxide as a main component on a substrate using amixed gas stream containing a metal chloride, an oxidizing material, andhydrogen chloride by a thermal decomposition method at a film depositionrate of 4500 nm/min. or greater, characterized by performing at leastone of the following 1) and 2).

1) Prior to mixing the metal chloride and the oxidizing material in themixed gas stream, the hydrogen chloride is brought into contact with atleast one selected from the metal chloride and the oxidizing material.

2) A buffer layer is formed in advance on a surface of the substrate onwhich the thin film containing a metal oxide as the main component is tobe formed.

With this method, a thin film containing a metal oxide as the maincomponent can be formed over a large area and a long time at a high filmdeposition rate in a stable manner by a thermal decomposition method.Moreover, because a substrate according to this invention is providedwith a thin film containing a metal oxide as the main component in whichthe film thickness is uniform and the surface unevenness is relativelylarge, its resistivity is low, and it is unlikely to cause problems inits appearance such as white turbidity.

In 1) of the method of the present invention, it is sufficient thatbefore the metal chloride and the oxidizing material mix with each otherin the mixed gas stream, hydrogen chloride contacts at least oneselected from the metal chloride and the oxidizing material; forexample, the metal chloride and the oxidizing material may besuccessively or simultaneously added to a gas stream containing hydrogenchloride to form the mixed gas stream, or for example, hydrogen chloridemay be added in advance to both or either one of the metal chloride andthe oxidizing material.

Furthermore, since a photoelectric conversion device according to thisinvention is provided with the substrate having the above-notedcharacteristics, it has advantages such as it is unlikely to causedefects such as pinholes in the photoelectric conversion layer and thephotoelectric conversion efficiency is high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus used for an online CVD(Chemical Vapor Deposition) method.

FIG. 2 is a cross-sectional view of one example of a photoelectricconversion device to which this invention is applied.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinbelow, preferred embodiments of this invention are described indetail. It should be noted that the invention is not intended to belimited by the following preferred embodiments.

This invention is characterized by a method of forming a thin filmcontaining a metal oxide as the main component on a substrate using athermal decomposition method, which forms the thin film containing ametal oxide as the main component at a high film deposition rate whilesuppressing pipe clogging due to the reaction of a mixed gas of a metalchloride and an oxidizing material. Herein, the term “thin filmcontaining a metal oxide as the main component” is intended to mean athin film that contains a metal oxide such as tin oxide, titanium oxide,or silicon oxide, as its main component. The term “main component”denotes, according to convention, that the content of a compositionalcomponent is 50 wt. % or greater. The characteristics of a thin film aremostly determined by its main component, and therefore, it will beappropriate to assess the characteristics of the thin film with the maincomponent:

The present inventors have conducted intensive studies on a method forforming a thin film containing a metal oxide as the main component by athermal decomposition method stably over a large area and a long time ata high film deposition rate, 4500 nm/min. or greater, and as a resulthave found that if, before mixing a metal chloride and an oxidizingmaterial in a gas stream transferring raw materials onto a substrate,hydrogen chloride is added to the gas stream at an appropriate amount,or if the surface of a substrate on which the thin film is to be formedis made into a shape such that crystal growth takes place easily, thethin film containing a metal oxide as the main component is made to havea uniform film thickness and a relatively large surface roughness. Bypermitting hydrogen chloride to be present in advance in a gas streambefore mixing a metal chloride and an oxidizing material in this way,the function of suppressing the reaction between the metal chloride andthe oxidizing material is enhanced, so even if the concentration ofhydrogen chloride in the gas stream is kept low, the above-notedreaction effectively can be suppressed until the gas stream reaches thesubstrate. It is desirable that, before the metal chloride and theoxidizing material are mixed together, hydrogen chloride be mixed witheither of the raw materials. Also, by controlling the surface shape ofthe substrate on which the thin film containing a metal oxide as themain component is to be formed, the crystal growth of the metal oxidecan be allowed to start from numerous points, and variation in filmthickness can be suppressed even if the film deposition rate is madefaster.

When the mole ratio of hydrogen chloride to the metal chloride is highin the mixed gas stream, clogging of the pipe through which the mixedgas passes does not easily occur, but additionally, the reaction betweenthe metal chloride and the oxidizing material itself is suppressed;consequently, the film deposition rate for the thin film containing ametal oxide as the main component considerably decreases, or the thinfilm does not form finely. In view of this, it has been found that whenthe proportion of hydrogen chloride to the metal chloride is reduced toless than 1 in mole ratio, the thin film can be formed without cloggingthe pipe at a high film deposition rate of 4500 nm/min. or greater oreven at 6300 nm/min. or greater even if the mixed gas containing themetal chloride and an oxidizing material is supplied to form a thin filmcontinuously for a long time. In particular, it was found that settingthe mole ratio of hydrogen chloride to a metal chloride to be 0.2 orless is more effective.

The thin film containing a metal oxide as the main component may beformed directly on the substrate, or alternatively, it may be formed onan undercoating film provided on the substrate. When a buffer layer thatcontains a large quantity of what can serve as the starting points forcrystal growth of the metal oxide is allowed to exist on the substratein advance before the formation of the thin film containing a metaloxide as the main component, it is possible to suppress variation in thecrystal growth over the entire thin film and to make the film thicknessuniform and the surface roughness relatively large.

This “buffer layer” denotes those in which fine metallic particles areadhered to a substrate, or a thin film that is formed at a slower filmdeposition rate than the film deposition rate for the thin filmcontaining a metal oxide as the main component. Generally, in thermaldecomposition methods, the formation of the thin film virtually denotescrystal growth in the case where the metal oxide is crystalline;therefore, the conditions of the crystal growth in the thin film changeconsiderably depending on the conditions of the surface of the substrateor the like on which the thin film is formed. Specifically, if whatserves as starting points for crystal growth exist in large numbers onthe surface of a substrate on which the thin film is formed, crystalgrowth starts from numerous points, and consequently, the crystalgrowth, that is, the thickness of the thin film, becomes relativelyuniform. On the other hand, if what serves as starting points for thecrystal growth exist in fewer numbers on that surface, each one of thecrystals grows large before the formation of crystal nuclei in the caseof a raw material with faster reactivity being used, and variation infilm thickness therefore becomes large. Moreover, crystals become moredifficult to grow, slowing down the film deposition rate. In turn, ifthe formation temperature of the thin film is increased to complementthe slowing down of the film deposition rate, the variation in filmthickness becomes even larger. In view of this, by providing the bufferlayer on the substrate in advance, the crystal growth can be startedfrom numerous points in the thin film having a metal oxide as the maincomponent and the film thickness of the thin film having a metal oxideas the main component can be made uniform even at a high film depositionrate.

For the fine metallic particles that constitute the buffer layer, it ispreferable that their average particle diameter be 5 to 500 nm in orderthat they function as nuclei for crystal growth and suppress theformation of giant crystal grains at the same time in the formation ofthe thin film containing a metal oxide as the main component. The methodfor providing the fine metallic particles on the substrate is notparticularly limited, but a preferable method is such that they arefixed to a substrate heated at a high temperature by a powder sprayingmethod, in order that they can be disposed uniformly over the substrateand not be overlaid. It is desirable that the fine metallic particlesform a single layer and have a closest packed structure on a substrate;however, there may be slight gaps between the particles because it issufficient as long as they function as the nuclei for crystal growth.When the gap between the particles is 100 μm or less, the particles cancontribute to uniformity in the thin film containing a metal oxide asthe main component.

Because the thin film that constitutes the buffer layer needs tofunction as starting points for crystal growth in the thin filmcontaining a metal oxide as the main component, it is necessary that thefilm be formed uniformly on the surface of the substrate or of theundercoating film, desirably with bumps at constant intervals on thesurface. For that reason, the film deposition rate for this thin film isslower than the film deposition rate for the thin film containing ametal oxide as the main component. Even if the film deposition rate forthis thin film itself is slow, the thickness thereof is, as will bedescribed later, significantly thinner than that of the thin filmcontaining a metal oxide as the main component; therefore, the filmdeposition rate as a whole, which includes that for the thin filmcontaining a metal oxide as the main component, does not degradeconsiderably. Rather, because of the presence of this thin film, thefilm deposition rate for the thin film containing a metal oxide as themain component can be made faster; therefore, if the buffer layer isformed to be relatively thin and in addition the thin film containing ametal oxide as the main component is formed more quickly at a highertemperature, the film deposition rate as a whole can be made faster.

Because of the presence of the buffer layer, the starting points forcrystal growth of metal oxide increase greatly in number and the crystalgrowth starts almost simultaneously from numerous positions; therefore,the generation of giant crystal grains is suppressed, and as a result,the thickness of the thin film containing a metal oxide as the maincomponent becomes relatively uniform. When the buffer layer is the sametype of thin film as the thin film containing a metal oxide as the maincomponent, a high film deposition rate can be maintained whilepreventing clogging of a pipe by making a mixture so that the mole ratioof hydrogen chloride to a metal chloride in the mixed gas stream is lessthan 1 in the formation of the buffer layer as well.

The undercoating film serves to prevent, for example, when the substrateis glass, an alkaline component contained in the glass from thermallydiffusing in the buffer layer or the thin film containing a metal as themain component, and examples include thin films containing siliconoxide, aluminum oxide, silicon oxynitride, silicon oxycarbide, or thelike as the main component. Alternatively, when the bond strengthbetween the substrate and either the buffer layer or the thin filmcontaining a metal oxide as the main component is low, it may be such athin film that contains both of the components of the substrate andeither the buffer layer or the thin film containing a metal oxide as themain component. Because of the presence of the undercoating layer, thebuffer layer or the thin film containing a metal oxide as the maincomponent can be bonded to the substrate at a sufficient strength, andits characteristics do not easily degrade. Further, the undercoatingfilm may be a single layer, or may be made up of two layers. Forexample, in cases where the undercoating film is made up of two layers,if a thin film having a thickness of 20 to 100 nm and containing tinoxide or titanium oxide as the main component is used for a firstundercoating layer that is nearer the substrate whereas a thin filmhaving about the same thickness and containing silicon oxide or aluminumoxide as the main component is used for a second undercoating layer,interference colors originating from the thin film containing a metaloxide as the main component can be reduced.

In particular, when the undercoating film includes two layers, theformation of a thin film containing a metal oxide such as tin oxide ortitanium oxide as the main component for the first undercoating layermakes it possible to increase the film deposition rate for the thin filmcontaining a metal oxide as the main component that is directly formedon the second undercoating layer, or to increase the film thickness ofthe thin film containing a metal oxide as the main component withoutcausing a white turbidity condition. The thin film containing a metaloxide such as tin oxide or titanium oxide as the main component that isused for the first undercoating layer is crystalline, even though it isa very thin film, and a surface roughness originating from crystalgrains is formed on the surface thereof. This surface roughness isreflected in the surface of the non-crystalline second undercoatinglayer, such as silicon oxide or aluminum oxide. For this reason, if theundercoating film is only a non-crystalline undercoating film, such assilicon oxide, the surface becomes completely flat, but since thesurface roughness is formed on the surface of the undercoating film, thesurface roughness serves to function as starting points for growing thebuffer layer or the thin film containing a metal oxide as the maincomponent, exhibiting various similar advantageous effects to those ofthe above-described buffer layer.

On the other hand, even if the substrate was glass, the undercoatingfilm is not necessarily required when the substrate is aluminosilicateglass, borosilicate glass, quartz glass, or the like, which does notcontain alkaline components. Nevertheless, there are cases in which theundercoating film is necessary for other purposes than preventing analkaline component from diffusing, and it should not be interpreted asexcluding the provision of the undercoating film on a glass that doesnot contain alkaline components.

Those glasses that do not contain alkaline components have higherthermal characteristics, such as glass transition temperature, than asoda lime glass, which contains an alkaline component, and therefore,they are capable of forming a thin film containing a metal oxide as themain component at higher temperatures.

The metal that constitutes the buffer layer may be a different type ofmetal from the metal of the thin film containing a crystalline metaloxide as the main component, but it is preferable that they are the sametype of metal. When they are the same type of metal, crystal growth isinduced more in the thin film containing a metal oxide as the maincomponent, and therefore, the fine metallic particles can be made smallin particle diameter or less in number, or the content of the metal canbe reduced in the buffer layer. For example, when a thin film made oftin oxide or titanium oxide that has a rutile structure is formed as thebuffer layer, it is desirable to form a film composed of tin oxide ortitanium oxide with the same rutile structure, or a film composed oftitanium oxide with an anatase structure, which is very similar to therutile structure, as the thin film containing a metal oxide as the maincomponent.

The method for forming the thin film containing a metal oxide as themain component is not particularly limited as long as it is a thermaldecomposition method, and examples include a CVD method and asolution-spraying method in which a solution material is sprayed onto aheated substrate. If the buffer layer and the thin film containing ametal oxide as the main component are formed by the same formationmethod, they can be formed within a short time by a series ofmanufacturing steps; for this reason, it is preferable that these beformed by the same method in terms of industrial production efficiency.An example is a method in which, after forming the buffer layer using aCVD method, the thin film containing a metal oxide as the main componentis successively formed. In this case, however, the formation temperaturefor the thin film containing a metal oxide as the main component becomeslower than that in the formation of the buffer layer, and therefore, itis desirable to utilize a material with good reactivity, such as atetrachloride, for the raw material of the thin film containing a metaloxide as the main component.

Preferable materials for the thin film containing a metal oxide as themain component are chlorides of metals that do not contain organicsubstances, such as tin dichloride, tin tetrachloride, titaniumchloride, zinc chloride, and indium chloride, which are chemicallystable and have low environmental load, and tetrachloride of metal isespecially suitable to increase the film deposition rate.

When the concentration of the metal in a gas flow containing the rawmaterial was lowered, it was confirmed that in the case of forming thethin film that constitutes the buffer layer by a CVD method, the filmdeposition rate for the buffer layer could be made faster and moreoverwhite turbidity was not caused even with the buffer layer having anincreased film thickness. It is inferred that this is because thelowering of the concentration of the metal in the gas flow suppressed anabrupt crystal growth that originates from the high concentration metalresiding locally.

The thin film that constitutes the buffer layer should preferably be ina condition such that the thickness is 10 to 250 nm and the surfacethereof has a multiplicity of bumps having a height of 10 to 200 nm.When the thickness is less than 10 nm, there is a risk of theundercoating film being not completely covered; on the other hand, whenexceeding 250 nm, the bumps become too large and too high, increasingthe risk of generating giant crystal grains in the thin film containinga metal oxide as the main component. The more preferable thickness ofthis thin film is 30 to 200 nm.

The metal chloride that is a raw material for the thin film containing ametal oxide as the main component preferably should be in a gaseousstate in the vicinity of the substrate. Accordingly, it may be in aliquid state on the way in which it is supplied to the vicinity of thesubstrate. That is, it is possible to employ either a solution-sprayingmethod, in which the gas stream containing the metal chloride is liquidon the way, or a powder spraying method, in which it is in a solidstate.

With a thin film-forming method according to the this invention, thepipe through which the mixed gas stream passes is not clogged up even ifthe thin film containing a metal oxide as the main component iscontinuously formed at a film deposition rate of 4500 nm/min. orgreater. In particular, in the method in which the undercoating film,the thin film that constitutes a buffer layer, and the thin filmcontaining a metal oxide as the main component are formed in that orderin a float bath by a CVD method using a glass ribbon as a substrate(hereafter referred to as a “online CVD method”), the temperature of thereaction system in the formation of the thin film containing a metaloxide as the main component (the surface temperature of the glass ribbonimmediately therebefore) can be elevated to 615° C. or higher, or evento a range of 620° C. to 750° C., and when the above-noted surfacetemperature is 650° C. or higher, the film deposition rate reaches ashigh as 6300 to 20000 nm/min.

As the chlorides of metals that are raw materials for the thin film thatconstitutes the buffer layer or the thin film containing a metal oxideas the main component, chlorides of tin and chlorides of titanium arepreferable. Examples of tin materials include tin tetrachloride,dimethyltin dichloride, dibutyltin dichloride, tetramethyltin,tetrabutyltin, dioctyltin dichloride, monobutyltin trichloride, anddibutyltin diacetate, and tin tetrachloride is particularly suitable.Examples of titanium material include titanium tetrachloride, titaniumisopropoxide, and the like.

In addition, examples of the oxidizing material that reacts with theabove-noted metal chloride and that constitutes the thin film containinga metal oxide as the main component include oxygen, water vapor, and dryair.

Further; when a thin film having tin oxide as the main component isformed as the thin film containing a metal oxide as the main component,it is possible to add chemical compounds of antimony or fluorine in themixed gas stream in order to improve its conductivity. Examples of thechemical compound of antimony include antimony trichloride and antimonypentachloride, and examples of the fluorine compound include hydrogenfluoride, trifluoroacetic acid, bromotrifluoromethane, andchlorodifluoromethane.

In the case of forming the undercoating film by a thermal decompositionmethod, examples of raw materials for silicon oxide suitable as theundercoating film include monosilane, disilane, trisilane,monochlorosilane, dichlorosilane, 1,2-dimethylsilane,1,1,2-trimethyldisilane, 1,1,2,2-tetramethyldisilane, tetramethylorthosilicate, and tetraethyl orthosilicate. Examples of the oxidizingmaterials in this case include oxygen, water vapor, dry air, carbondioxide, carbon monoxide, nitrogen dioxide, and ozone. It should benoted that in the case of using silane, an unsaturated hydrocarbon gas,such as ethylene, acetylene, or toluene, may be used in combination forthe purpose of preventing the silane from reacting before reaching theglass surface. Likewise, examples of aluminum materials for depositingaluminum oxide suitable for the undercoating film includetrimethylaluminum, aluminum triisopropoxide, diethylaluminum chloride,aluminum acetylacetonate, and aluminum chloride. Examples of theoxidizing materials in this case include oxygen, water vapor, and dryair.

Hereinbelow, a preferred embodiment with an online CVD method isdescribed in more detail. As illustrated in FIG. 1, in an apparatus usedfor the online CVD method, a glass ribbon 10 flows out from a meltingfurnace (float furnace) 11 into a float bath 12 and moves on a tin bath15 in a belt-like form, and a predetermined number of coaters 16 (threecoaters 16 a, 16 b, and 16 c in the embodiment illustrated in thefigure) are disposed in the tin float bath so that they are spaced apartfrom the surface of the glass ribbon. From these coaters, gaseous rawmaterials are supplied so that the undercoating film, themetal-containing thin film, and the thin film containing a crystallinemetal oxide as the main component are formed successively on the glassribbon 10. Although not shown in the figure, it is possible to providemore coaters so that the undercoating film may include two layers, orthe thin film containing a crystalline metal oxide as the main componentmay be formed by supplying raw materials from a plurality of coaters.The glass ribbon 10 on which the thin film containing a crystallinemetal oxide as the main component is formed is pulled up by rollers 17and is transferred to an annealing furnace 13. The glass ribbon that hasbeen annealed in the annealing furnace 13 is cut into glass sheetshaving a predetermined size by a cutting device, which is not shown inthe figure. For the formation of the thin film containing a metal oxideas the main component, it is possible to use a spraying method for theglass ribbon that has come out of the float bath 12 in combination withthe CVD method in the float bath.

With the thin film-forming method according to this invention, in anonline CVD method too, even when the thin film containing a metal oxideas the main component is formed on a substrate by a thermaldecomposition method using a mixed gas stream containing a metalchloride, an oxidizing material, and hydrogen chloride at a filmdeposition rate of 4500 nm/min. or greater for a long time continuously,the pipe through which the mixed gas stream passes is not clogged up. Inaddition, the use of the above-noted mixed gas stream has manyadvantages in terms of industrial manufacturing process such astemperature controls are made simple until they are supplied to thecoaters.

Hereinbelow, an example of a photoelectric conversion element employinga substrate provided with the buffer layer and the transparentconductive film is described with reference to FIG. 2. The photoelectricconversion element is obtained by forming, on a substrate 30,undercoating films 31 and 32 if necessary, a buffer layer 33, a thinfilm containing a metal oxide as the main component (transparentconductive film) 34, photoelectric conversion layers 37 and 38, whichare thin films composed of amorphous silicon or crystalline silicon orsimilar films, and a conductive film (back electrode) 35 successively. Adevice in which the photoelectric conversion element is incorporated andvarious components are associated and assembled into an unit so that,for example, as a solar cell, electric energy can be taken out fromlight energy, is referred to as a photoelectric conversion device.

The photoelectric conversion layer may be a single layer, or a pluralityof layers may be stacked. It may be a thin film composed of conventionalamorphous silicon, or may be a thin film composed of crystallinesilicon. Further, a thin film 37 composed of amorphous silicon and athin film 38 composed of crystalline silicon are combined to form aso-called tandem type. In the case of tandem type, generally, a thinfilm composed of amorphous silicon is formed on the transparentconductive film, and a thin film composed of crystalline silicon isformed thereover.

The thin film composed of amorphous silicon is formed by depositing p-,i-, and n-type semiconductor layers in that order by a plasma CVDmethod. Specifically, examples include a film in which the followinglayers are deposited in that order: a p-type microcrystallinesilicon-based layer doped with boron atoms, which areconductivity-determining impurity atoms, at 0.01 atom % or more; anintrinsic non-crystalline silicon layer, serving as a photoelectricconversion layer; and an n-type microcrystalline silicon-based layerdoped with phosphorus atoms, which are conductivity-determining impurityatoms, at 0.01% or more. Nevertheless, these respective layers are notlimited to the foregoing, and for example, it is possible to use anon-crystalline silicon-based layer for the p-type layer, or to usealuminum as the impurity atoms in the p-type microcrystallinesilicon-based layer. Further, alloy materials of non-crystalline ormicrocrystalline silicon carbide or silicon germanium may be used as thep-type layer. The film thickness of the conductive-type (p-type, n-type)microcrystalline silicon-based layer should preferably be 3 to 100 nm,or more preferably 5 to 50 nm. The film thickness of the intrinsicnon-crystalline silicon layer should preferably be 0.05 to 0.5 μm. In aphotoelectric conversion element provided with a thin film composed ofamorphous silicon, however, it is possible to employ a non-crystallinesilicon carbide layer (e.g., a non-crystalline silicon carbide layercomposed of non-crystalline silicon containing 10 atom % or less ofcarbon) or a non-crystalline silicon germanium layer (e.g., anon-crystalline silicon germanium layer composed of non-crystallinesilicon containing 30 atom % or less of germanium), which are alloymaterials, in place of the intrinsic non-crystalline silicon layer. Itis preferable that the intrinsic non-crystalline silicon layer bedeposited at a substrate temperature of 450° C. with a plasma CVDmethod. This layer is formed to be a thin film that is substantiallyintrinsic semiconductor, the density of theconductivity-type-determining impurity atoms of which is 1×10¹⁸ cm⁻³ orless.

The thin film composed of crystalline silicon can be formed bydepositing p-, i-, and n-type semiconductor layers in that order by aplasma CVD method in a similar procedure to that for the foregoing thinfilm composed of amorphous silicon. Alternatively, it can be formed byelectron beam vapor deposition using silicon as a raw material, a plasmaCVD method that utilizes glow discharge and uses monosilane diluted witha hydrogen gas as a raw material, or a thermal CVD method usingmonosilane or dichlorosilane. It is preferable that the film thicknessof the thin film composed of crystalline silicon be 0.1 to 10 μm, andparticularly preferably 5 μm or less. This thin film is formed at, forexample, a low temperature of 450° C. with the plasma CVD method andtherefore contains a relatively large number of hydrogen atoms forterminating or inactivating grain boundaries and defects in the grains.The hydrogen content in the layer is preferably in a range of 0.5 to 30atom %, and particularly preferably in a range of 1 to 20 atom %.

In the case of tandem-type photoelectric conversion element, thethickness of thin film composed of amorphous silicon is preferably 0.05to 0.4 μm, and the thickness of the thin film composed of crystallinesilicon is preferably 0.5 to 5 μm, although they may depend on theconfiguration of the photoelectric conversion device. For reference, thespectral sensitivity characteristic of the thin film composed ofamorphous silicon becomes greatest in a wavelength range of about 500 to600 nm, and it shows the sensitivity only in a wavelength range up toabout 800 nm due to the optical energy gap. On the other hand, the thinfilm composed of crystalline silicon shows the sensitivity up to about1100 nm.

For the back electrode, it is preferable to form at least one layer of ametallic layer composed of at least one material selected from aluminum(Al), silver (Ag), gold (Au), copper (Cu), platinum (Pt), and chromium(Cr) by a sputtering method or a vapor deposition method. Further, it ispossible to form a layer composed of conductive oxide such as ITO, tinoxide, or zinc oxide between the photoelectric conversion layer and theback electrode.

The photoelectric conversion element provided with the thin filmcomposed of crystalline silicon generates a lower open-end voltage and ahigher short circuit current density than that provided with the thinfilm composed of amorphous silicon. For that reason, in a photoelectricconversion device provided with the thin film composed of crystallinesilicon, the transmissivity of the transparent conductive film has moreinfluence on its photoelectric conversion efficiency than the sheetresistance value thereof.

EXAMPLES

Hereinbelow, this invention is described in detail with reference toexamples. It should be understood, however, that the invention is notintended to be limited by the following examples.

Example 1

A 1-mm thick aluminosilicate glass sheet cut into a size of 150×150 mmwas placed on a mesh belt and passed through a heating furnace to beheated to about 660° C. While transferring the heated glass sheetfurther, a mixed gas composed of tin tetrachloride (vapor), water vapor,hydrogen chloride, and nitrogen was supplied from a coater installedabove the transfer line so as to form, on the glass, a thin film (bufferlayer) having a film thickness of 110 nm and composed of tin oxide(SnO₂) at a film deposition rate of 2210 nm/min. A plurality of suchglasses for which the process was completed up to the buffer layer wereprepared. After annealing the glass sheet, it was again placed on themesh belt and was passed through the heating furnace to be heated toabout 660° C. The heated glass sheet was further transferred, and amixed gas composed of 2.1 mol % tin tetrachloride (vapor), 62.3 mol %water vapor, 0.1 mol % hydrogen chloride, nitrogen, and hydrogenfluoride was supplied from a coater installed above the transfer lineonto the buffer layer to form a transparent conductive film (thin filmcontaining a metal oxide as the main component) having a film thicknessof 1740 nm and composed of fluorine-containing tin oxide (SnO₂:F) at afilm deposition rate of 6480 nm/min. Hydrogen chloride was supplied bymixing it, in advance, with water vapor that had not yet been mixed withtin tetrachloride. The mole ratio of hydrogen chloride to tintetrachloride was 0.05. The gap between the coaters and the glass sheetwas set at 10 mm, and further, a nitrogen gas was supplied beside theexhaust section in a curtain-like fashion so that the outside air didnot intrude inside the coater during the formation of the transparentconductive film.

This glass sheet had a haze ratio (haze factor) of 19% but showed nowhite turbidity.

In addition, the mixed gas composed of tin tetrachloride (vapor), watervapor, hydrogen chloride, nitrogen, and hydrogen fluoride was suppliedfrom the coater for about 3 hours continuously. The glasses for whichthe process was completed up to the buffer layer were transferred fromtime to time to confirm the film deposition rate and the characteristicsof the transparent conductive film; the result was that the filmthickness of the transparent conductive film remained almost unchanged,that the film deposition rate did not decrease, and that the haze ratiochanged only in a range of 19 to 22%. After the supply of the mixed gasfor about 3 hours, the pipe through which the mixed gas stream waspassed through was observed, but neither adhering substance nor cloggedspot was observed in the pipe.

Example 2

A buffer layer was formed on a glass prepared in a similar manner toExample 1, under the same conditions as those in Example 1. This glasssheet again was placed on the mesh belt and was passed through theheating furnace to be heated to about 660° C. While transferring theheated glass sheet further, a mixed gas composed of 2.6 mol % tintetrachloride (vapor), 79.9 mol % water vapor, 0.79 mol % hydrogenchloride, nitrogen, and hydrogen fluoride was supplied from a coaterinstalled above the transfer line to form on the buffer layer atransparent conductive film (thin film containing a crystalline metaloxide as the main component) having a film thickness of 1700 nm andcomposed of fluorine-containing tin oxide (SnO₂:F) at a film depositionrate of 11400 nm/min. Hydrogen chloride was supplied by mixing it, inadvance, with water vapor that had not yet been mixed with tintetrachloride. The mole ratio of hydrogen chloride to tin tetrachloridewas 0.3. The gap between the coaters and the glass sheet was set at 10mm, and a nitrogen gas was supplied beside the exhaust section in acurtain-like fashion so that the outside air does not intrude inside thecoater during the formation of the transparent conductive film.

This glass sheet had a haze ratio of 20% but showed no white turbidity.

In a similar manner to Example 1, the mixed gas used for forming thetransparent conductive film was supplied from the coater for about 3hours continuously. The glasses for which the process was completed upto the buffer layer were transferred from time to time to confirm thefilm deposition rate and the characteristics of the transparentconductive film; the result was that the film thickness of thetransparent conductive film remained almost unchanged, that the filmdeposition rate did not decrease, and that the haze ratio of thetransparent electric film changed only in a range of 17 to 22%. Afterthe supply of the mixed gas for about 3 hours, the pipe was observed,but neither adhering substance nor clogged spot was observed in thepipe.

Example 3

A buffer layer was formed on a glass prepared in a similar manner toExample 1, under the same conditions as those in Example 1. This glasssheet was again placed on the mesh belt and was passed through theheating furnace to be heated to about 660° C. While transferring theheated glass sheet further, a mixed gas composed of 2.6 mol % tintetrachloride (vapor), 80.1 mol % water vapor, 0.53 mol % hydrogenchloride, nitrogen, and hydrogen fluoride was supplied from a coaterinstalled above the transfer line to form on the buffer layer atransparent conductive film (thin film containing a metal oxide as themain component) having a film thickness of 1650 nm and composed offluorine-containing tin oxide (SnO₂:F) at a film deposition rate of10800 nm/min.

Hydrogen chloride was supplied by mixing it, in advance, with watervapor that had not yet been mixed with tin tetrachloride. The mole ratioof hydrogen chloride to tin tetrachloride was 0.2. The gap between thecoater and the glass sheet was set at 10 mm, and a nitrogen gas wassupplied beside the exhaust section in a curtain-like fashion so thatthe outside air does not intrude inside the coater during the formationof the transparent conductive film.

This glass sheet had a haze ratio of 17% but showed no white turbidity.

In a similar manner to Example 1, the mixed gas used for forming thetransparent conductive film was supplied from the coater for about 3hours continuously. The glasses for which the process was completed upto the buffer layer were transferred from time to time to confirm thefilm deposition rate and the characteristics of the transparentconductive film; the result was that the film thickness of thetransparent conductive film remained almost unchanged, that the filmdeposition rate did not decrease, and that the haze ratio varied only ina range of 15 to 20%. After the supply of the mixed gas for about 3hours, the pipe was observed, but neither adhering substance nor cloggedspot was observed in the pipe.

Example 4

A buffer layer was formed on a glass prepared in a similar manner toExample 1, under the same conditions as those in Example 1. This glasssheet was again placed on the mesh belt and was passed through theheating furnace to be heated to about 660° C. While transferring theheated glass sheet further, a mixed gas composed of 3.0 mol % tintetrachloride (vapor), 76.8 mol % water vapor, 0.60 mol % hydrogenchloride, nitrogen, and hydrogen fluoride was supplied from a coaterinstalled above the transfer line to form on the buffer layer atransparent conductive film (thin film containing a metal oxide as themain component) having a film thickness of 2170 nm and composed offluorine-containing tin oxide (SnO₂:F) at a film deposition rate of11700 nm/min.

Hydrogen chloride was supplied by mixing it, in advance, with watervapor that had not yet been mixed with tin tetrachloride. The mole ratioof hydrogen chloride to tin tetrachloride was 0.2. The gap between thecoater and the glass sheet was set at 10 mm, and a nitrogen gas wassupplied beside the exhaust section in a curtain-like fashion so thatthe outside air does not intrude inside the coater during the formationof the transparent conductive film.

This glass sheet had a haze ratio of 21% but showed no white turbidity.

In a similar manner to Example 1, the mixed gas used for forming thetransparent conductive film was supplied from the coater for about 3hours continuously. The glasses for which the process was completed upto the buffer layer were transferred from time to time to confirm thefilm deposition rate and the characteristics of the transparentconductive film; the result was that the film thickness of thetransparent conductive film remained almost unchanged, that the filmdeposition rate did not decrease, and that the haze ratio varied only ina range of 20 to 25%. After the supply of the mixed gas for about 3hours, the pipe was observed, but neither adhering substance nor cloggedspot was observed in the pipe.

Example 5

An undercoating film, a buffer layer, and a transparent conductive filmwere formed on a glass ribbon in that order utilizing an online CVDmethod. Specifically, 98 volume % of nitrogen and 2 volume % of hydrogenwere supplied inside the space of a float bath so that the inside of thefloat bath is kept at a slightly higher pressure than that outside thebath. With the inside of the float bath being kept to be a non-oxidizingatmosphere, a mixed gas composed of tin tetrachloride (vapor), watervapor, hydrogen chloride, nitrogen, and helium was supplied from a firstcoater located on the most upstream side to form a thin film (firstundercoating layer) having a thickness of 55 nm and composed of tinoxide on the glass ribbon. Subsequently, a mixed gas composed ofmonosilane, ethylene, oxygen, and nitrogen was supplied from a secondcoater to form a thin film (second undercoating layer) having athickness of 30 nm and composed of silicon oxide on the firstundercoating layer. Further, a mixed gas composed of 0.53 mol % tintetrachloride (vapor), 42.4 mol % water vapor, 0.03 mol % hydrogenchloride, and nitrogen was supplied from a third coater to form a thinfilm (buffer layer) having a thickness of 90 nm and composed of tinoxide (SnO₂) on the second undercoating layer having a surfacetemperature 680° C. at a film deposition rate of 1830 nm/min. Using acoater installed on the further downstream side, a mixed gas composed of3.4 mol % tin tetrachloride (vapor), 51.6 mol % water vapor, 0.18 mol %hydrogen chloride was supplied onto the buffer layer having a surfacetemperature of 630° C. to form a transparent conductive film (thin filmcontaining a metal oxide as the main component) having a film thicknessof 705 nm and composed of fluorine-containing tin oxide (SnO₂:F) at afilm deposition rate of 6980 nm/min.

This glass sheet had a haze ratio of 16% and showed no white turbidity.

Hydrogen chloride was supplied by mixing it, in advance, with watervapor that had not yet been mixed with tin tetrachloride. The mole ratioof hydrogen chloride to tin tetrachloride was 0.05.

Using a thin film-forming apparatus according to this online CVD method,the mixed gas used for forming the transparent conductive film wassupplied from the coater for about 4 hours continuously to confirm thefilm deposition rate and the characteristics of the transparentconductive film. The result was that the thickness of the transparentconductive film remained almost unchanged, the film deposition rate didnot decrease, and the haze ratio of the transparent conductive filmvaried only in a range of 14 to 20%. When the pipe was observed afterthe supply of the mixed gas for about 4 hours, a little adheringsubstance was observed but no clogged spot was found in the pipe.

Example 6

An undercoating film, a buffer layer, and a transparent conductive filmwere formed on a glass ribbon in that order utilizing an online CVDmethod. Specifically, 98 volume % of nitrogen and 2 volume % of hydrogenwere supplied inside the space of a float bath so that the inside of thefloat bath is kept at a slightly higher pressure than that outside thebath. With the inside of the float bath being kept as a non-oxidizingatmosphere, a mixed gas composed of tin tetrachloride (vapor), watervapor, hydrogen chloride, nitrogen, and helium was supplied from a firstcoater located on the most upstream side to form a thin film (firstundercoating layer) having a thickness of 55 nm and composed of tinoxide on the glass ribbon. Subsequently, a mixed gas composed ofmonosilane, ethylene, oxygen, and nitrogen was supplied from a secondcoater to form a thin film (second undercoating layer) having athickness of 30 nm and composed of silicon oxide on the firstundercoating layer. Further, a mixed gas composed of 1.20 mol % tintetrachloride (vapor), 36.2 mol % water vapor, 0.06 mol % hydrogenchloride, and nitrogen was supplied from a third coater to form a thinfilm (buffer layer) having a thickness of 170 nm and composed of tinoxide (SnO₂) on the second undercoating layer having a surfacetemperature 680° C. at a film deposition rate of 3365 nm/min. Using acoater installed on the further downstream side, a mixed gas composed of3.4 mol % tin tetrachloride (vapor), 51.6 mol % water vapor, 0.18 mol %hydrogen chloride, nitrogen, and hydrogen fluoride was supplied onto thebuffer layer having a surface temperature of 630° C. to form atransparent conductive film (thin film containing a metal oxide as themain component) having a film thickness of 675 nm and composed offluorine-containing tin oxide (SnO₂:F) at a film deposition rate of 6677nm/min.

This glass sheet had a haze ratio of 22% and showed no white turbidity.

Hydrogen chloride was supplied by mixing it, in advance, with watervapor that had not yet been mixed with tin tetrachloride. The mole ratioof hydrogen chloride to tin tetrachloride was 0.05.

In a similar manner to Example 5, the mixed gas used for forming thetransparent conductive film was supplied from the coater for about 4hours continuously to confirm the film deposition rate and thecharacteristics of the transparent conductive film. The result was thatthe thickness of the transparent conductive film remained almostunchanged, the film deposition rate did not decrease, and the haze ratioof the transparent conductive film varied only in a range of 18 to 23%.When the pipe was observed after the supply of the mixed gas for about 4hours, a little adhering substance was observed but no clogged spot wasfound in the pipe.

Example 7

A buffer layer and a transparent conductive film were formed on a glassribbon in that order utilizing an online CVD method. Specifically, 98volume % of nitrogen and 2 volume % of hydrogen were supplied inside thespace of a float bath so that the inside of the float bath is kept at aslightly higher pressure than that outside the bath. With the inside ofthe float bath being kept as a non-oxidizing atmosphere, a mixed gascomposed of 1.32 mol % tin tetrachloride (vapor), 39.4 mol % watervapor, 0.07 mol % hydrogen chloride, and nitrogen was supplied from afirst coater located on the most upstream side to form a thin film(buffer layer) having a thickness of 140 nm and composed of tin oxide(SnO₂) on the glass ribbon having a surface temperature 680° C. at afilm deposition rate of 2771 nm/min. Using a coater installed on thefurther downstream side, a mixed gas composed of 2.7 mol % tintetrachloride (vapor), 80.6 mol % water vapor, 0.54 mol % hydrogenchloride, nitrogen, and hydrogen fluoride was supplied onto the bufferlayer having a surface temperature of 630° C. to form a transparentconductive film (thin film containing a metal oxide as the maincomponent) having a film thickness of 798 nm and composed offluorine-containing tin oxide (SnO₂:F) at a film deposition rate of 5423nm/min.

This glass sheet had a haze ratio of 20% and showed no white turbidity.

Hydrogen chloride was supplied by mixing it, in advance, with watervapor that had not yet been mixed with tin tetrachloride. The mole ratioof hydrogen chloride to tin tetrachloride was 0.2.

In a similar manner to Example 5, the mixed gas used for forming thetransparent conductive film was supplied from the coater for about 4hours continuously to confirm the film deposition rate and thecharacteristics of the transparent conductive film; the result was thatthe thickness of the transparent conductive film remained almostunchanged, the film deposition rate did not decrease, and the haze ratioof the transparent conductive film varied only in a range of 16 to 32%.When the pipe was observed after the supply of the mixed gas for about 4hours, a little adhering substance was observed but no clogged spot wasfound in the pipe.

Comparative Example 1

A transparent conductive film was formed under the same conditions as inExample 5 except that the mixed gas was supplied without mixing hydrogenchloride therein. The formation within a short time resulted in atransparent conductive film having a surface roughness that is somewhatlarge and has variations, due to a slightly larger film thickness thanthat of Example 5. Also, when the mixed gas was supplied for 3 hourscontinuously, the pressure in the pipe increased and the supply of themixed gas became impossible. At this time, the pipe for the mixed gaswas disassembled to observe the inside, and consequently, it wasconfirmed that a white, adhering substance was formed inside the pipeand that the pipe was almost in a clogged state.

Comparative Example 2

A transparent conductive film was formed in a similar manner to Example2 except that the following points were changed. Taking Example D of JP9(1997)-40442 A as a reference, the mole ratio of hydrogen chloride totin tetrachloride was increased to 1.1. As a result, it was confirmedthat the thickness of the transparent conductive film excluding thebuffer layer was 200 nm and the film deposition rate was reduced toabout ⅓, that is, 2030 nm/min.

Manufacturing Example 1

Thin films having a thickness of 0.3 μm and composed of amorphoussilicon were formed on the respective transparent conductive filmsformed according to Example 1 and Comparative Example 1 by a plasma CVDmethod using monosilane and hydrogen as raw materials. Thereafter, asilver thin film (back electrode) having a thickness of 300 nm wasformed by a sputtering method, and thus, samples of a photoelectricconversion element were fabricated. These samples are configured inaccordance with a general configuration of a solar cell that uses a thinfilm composed of amorphous silicon as the photoelectric conversionlayer. For these samples, their photoelectric conversion efficiency wasmeasured by a known technique. The result was that the conversionefficiency of Example 1 was 9.4%, and that the conversion efficiency ofcomparative Example 1 was 8.65%.

According to this invention, a thin film containing a metal oxide as themain component can be formed at a high film deposition rate over a longtime. Furthermore, a high quality thin film containing a metal oxide asthe main component can be attained, and utilizing this, a photoelectricconversion device with a high conversion efficiency can be obtained.

1-9. (canceled)
 10. A substrate having a thin film, comprising asubstrate, a buffer layer formed on the substrate, and a thin film thatis formed on the buffer layer and contains a metal oxide as the maincomponent, wherein the buffer layer has bumps on its surface of the thinfilm side, and the bumps have a height of 10 to 200 nm.
 11. Thesubstrate having a thin film according to claim 1, wherein a metal oxideor fine metallic particles constitute the buffer layer.
 12. Thesubstrate having a thin film according to claim 2, wherein the bufferlayer and the thin film contain the same type of metal oxide.
 13. Thesubstrate having a thin film according to claim 1, wherein the bufferlayer has the thickness of 10 to 250 nm.
 14. The substrate having a thinfilm according to claim 1, wherein the substrate further comprises anundercoating film formed between the substrate and the thin film. 15.The substrate having a thin film according to claim 5, wherein theundercoating film includes the first undercoating layer formed on thesubstrate and the second undercoating layer formed on the firstundercoating layer.
 16. The substrate having a thin film according toclaim 6, wherein the second undercoating layer contains silicon oxide oraluminum oxide as the main component.
 17. The substrate having a thinfilm according to claim 7, wherein the silicon oxide is non-crystallinesilicon oxide and the aluminum oxide is non-crystalline aluminum oxide.18. The substrate having a thin film according to claim 6, wherein thefirst undercoating layer contains tin oxide or titanium oxide as themain component, and the second undercoating layer contains silicon oxideor aluminum oxide as the main component.
 19. The substrate having a thinfilm according to claim 9, wherein the silicon oxide is non-crystallinesilicon oxide and the aluminum oxide is non-crystalline aluminum oxide.20. The substrate having a thin film according to claim 5, wherein theundercoating film contains silicon oxide, aluminum oxide, siliconoxynitride, silicon oxycarbide, tin oxide or titanium oxide as the maincomponent.
 21. The substrate having a thin film according to claim 2,wherein the buffer layer contains at least one material selected fromtin oxide with a rutile structure, titanium oxide with a rutilestructure and titanium oxide with an anatase structure as the metaloxide.
 22. The substrate having a thin film according to claim 1,wherein the buffer layer is formed at a slower film deposition rate thanthe film deposition rate for the thin film.
 23. The substrate having athin film according to claim 1, wherein the buffer layer is formedthrough a chemical vapor deposition method.
 24. The substrate having athin film according to claim 14, wherein the buffer layer is formedthrough an online chemical vapor deposition method.
 25. The substratehaving a thin film according to claim 1, wherein the thin film is formedusing a mixed gas stream containing a metal chloride, an oxidizingmaterial, and hydrogen chloride by a thermal decomposition method at afilm deposition rate of 4500 nm/min. or greater.
 26. A photoelectricconversion device comprising the substrate having a thin film accordingto claim 1.